Synchronized switch harvesting applied to selfpowered smart systems: Piezoactive microgenerators for autonomous wireless transmitters

This paper discusses the design and integration of microgenerators, which directly convert mechanical energy into electrical energy, using our synchronized switch harvesting (SSH) method. This original method is based on the nonlinear processing of the piezoelement voltage, to optimize the energy extraction from the mechanical stresses. The final goal of the present contribution is to implement a SSH microgenerator to power a single autonomous wireless transmitter (AWT) that can be used in health monitoring networks and that is wireless, and truly selfpowered. Indeed, as it does not use any primary or rechargeable batteries, there is no need for element reloading or replacement of such elements. This increases the reliability by suppressing power supplies and data transmission wiring. In the proposed configuration, the AWT can harvest an energy quantity of approximately 20 mJ (for a 1.5 MPa lateral stress on the piezoelement) with a 470 mu F storage capacitor. This corresponds to a power density close to 6 mW/cm(3). Typically, a realistic target value of the density of harvested energy is 1 mu J x cm(-3) x mu def(-1)/cycle. (c) 2007 Elsevier B.V. All rights reserved.